The need for variable ratio lever assemblies has been recognized in the art of making brake pedal assemblies because of the increasing braking load that the operator experiences as the brake pedal is depressed. However, such pedal assemblies, because of the desire for a continuously increasing mechanical advantage, have used a fixed pedal pivot with a camming arrangement to shift the length of the level arms (see U.S. Pat. Nos. 4,069,722; 3,938,407; and 3,410,152). The use of cams to change the mechanical advantage of an accelerator pedal assembly would be undesirable because it requires a stationary pivot which, in turn, does not allow maintaining the required, greater mechanical advantage through the first arc of movement of the accelerator arm.
The operating conditions for an accelerator pedal assembly differ from that of braking assemblies. It is desirable that the mechanical advantage shift from a high to a lower value as the pedal is depressed, this permits a slower throttle opening rate in the first stages of the pedal movement followed by a faster throttle opening rate when the pedal approaches wide open throttle (WOT). Secondly, the travel for an accelerator pedal operating on two or more lever ratios should travel through a distance no greater than that required for a conventional accelerator pedal moving about a single fixed pivot at a unitary mechanical advantage. Thirdly, the change in mechanical advantage should occur as a discrete stepped increment rather than a continuous, unnoticeable variable, this provides a feedback signal to the operator telling him when high fuel consumption conditions are being experienced.
The desire for an initially slow rate of throttle opening followed by a faster rate when approaching WOT has been entertained in U.S. Pat. Nos. 3,490,294 and 3,264,896. However, in each of these patents cams were used to impart a gradual change in the mechanical advantage by (a) changing the effective length of a lever, other than the accelerator pedal, or (b) by changing the lever length of the accelerator pedal without affecting the fulcrum of the pedal itself. Both approaches are costly and do not provide for a sufficient degree of change in the mechanical advantage to be worthwhile.
U.S. Pat. No. 3,646,830 discloses a braking assembly that has used a concept of two lever ratios shifting between two discrete fulcrums. The shift is brought about by the use of a complex set of links that do not stay in position unless some residual pedal force is constantly applied which in turn affects pedal effort.